Field of the Invention
Embodiments described herein relate generally to a charged particle beam lithography method and a charged particle beam lithography apparatus, and relates to a method relating to adjustment of the resolution of an electron beam in an electron beam lithography apparatus that irradiates the electron beam onto a target object.
Related Art
In recent years, circuit line widths of semiconductor devices are getting still smaller in accordance with high level integration of an LSI. As a method of forming an exposure mask (also referred to as a reticle) for forming circuit patterns on semiconductor devices, an electron beam (EB) lithography technique having an excellent resolution is used.
FIG. 11 is a conceptual view for describing operation of a variable-shaped electron beam lithography apparatus. The variable-shaped electron beam lithography apparatus operates as follows. A first aperture plate 410 is formed with a rectangular opening 411 for forming an electron beam 330. In addition, a second aperture plate 420 is formed with a variable-shaping opening 421 for forming the electron beam 330, which has passed through the opening 411 in the first aperture plate 410, into a desirable rectangular shape. The electron beam 330, which has been irradiated from a charged particle source 430 and has passed through the opening 411 in the first aperture plate 410, is deflected by a deflector, passes through a portion of the variable-shaping opening 421 in the second aperture plate 420, and is irradiated to a target object 340 placed on a stage moving continuously in one predetermined direction (set to X direction, for example). Specifically, a rectangular shape that can pass through both of the opening 411 in the first aperture plate 410 and the variable-shaping opening 421 in the second aperture plate 420 is written on a writing region of the target object 340 placed on the stage moving continuously in X direction. A method for forming an arbitrary shape by causing a beam to pass through both of the opening 411 in the first aperture plate 410 and the variable-shaping opening 421 in the second aperture plate 420 is referred to as a variable-shaping beam method (VSB method).
In the electron beam lithography, great importance is placed on throughput for mask production. However, for various types of evaluation for next-generation lithography development, finer pattern formation is required. Specifically, in such a case, great importance is placed on resolution of a beam.
Increasing beam current density is effective to increase throughput, but increases beam current. Thus, a beam resolution is typically lowered due to Coulomb effect. Coulomb effect largely depends on beam current. Therefore, when the beam current density is low under condition where a beam profile along the orbit is the same, the beam current becomes small, and influence of Coulomb effect becomes small to improve resolution. On the other hand, when the current density is high, influence of Coulomb effect becomes large to deteriorate the resolution.
The resolution also depends on a generation of a lithography apparatus. Lithography apparatuses of newer generations typically have a higher resolution than lithography apparatuses of older generations. However, lithography apparatuses of newer generations do not always write the most advanced pattern only. Those lithography apparatuses also write patterns of a lower resolution that were written in older generations.
As described above, the resolution of a beam unfortunately varies depending on conditions of the beam current or between different lithography apparatuses. Meanwhile, for a process performed on a target object after writing, such as etching, process conditions depending on the beam resolution upon writing is set. In other words, changing the resolution upon writing requires re-optimization of parameters of post processes. Thus, when importance is placed on processes, an identical resolution performance is required for various conditions of emission current, or for various lithography apparatuses.
There is disclosed a technique for forming a pattern having a symmetrical shape with respect to the center line between a first end and a second end by superimposing a beam having a beam profile that has different inclinations at the first end side and the second end side with a beam having abeam profile obtained by inversing the beam profile with the center line as the inversion axis and that has the identical size to the size of the original beam profile. According to the technique, the designed center position of the pattern is not shifted (as disclosed for example in JP-A-2009-054945).